With the development of economy, traffic network expands in various directions. A large number of privately-owned vehicles are used in people's daily life. However, many people with color vision deficiency cannot obtain a driver's license because of the restrictions of traffic rules. Also, because of the color vision deficiency or color blindness, these people encounter a lot of inconvenience when walking on the streets.
In 2003, the Visible Light Communications Consortium (VLCC) was founded. The VLCC has been widely promoting the use of flashing light-emitting diode (LED) light sources for data transmission, to implement visible light communication.
Compared to technologies such as cable communication and radio frequency (RF) communication, visible light communication has at least the following advantages. First, visible light communication does not require application for a spectrum authentication. In the field of communication, the available radio frequencies are already quite limited. Visible light communication based on, e.g., LED, does not have the frequency allocation problems in the radio frequency communication, and is less susceptible to interferences. Further, the spectral band of the communication signals used in the visible light communication is often in the range of about 380 nm to about 780 nm, which is safe to humans. The visible light communication can thus be used in an environment such as hospitals, and other places having strict requirements on electromagnetic interferences. Further, visible light communication is often easy to debug and easy to implement. In addition, visible light communication is often less costly.
There are many types of color vision deficiencies, among which the most common type is the red-green color blindness. In general, people with color blindness are not able to accurately identify traffic lights and the information delivered by the traffic lights. Color blindness generally has two symptoms. One symptom is that the patients confuse two different colors A and B. The patients may think A and B are the same color. For example, a patient with red-color blindness is not able to distinguish between red and dark green. Another symptom is that, the patients are not able to sense colors but can only sense different tones, i.e., different levels of brightness and darkness.
Thus, a visible light communication means to provide a system for identifying colors of traffic lights for those people with color vision deficiencies is desired.